Nervous System Chapter 35.2 Nervous System Notes Part 1: Neural Physiology Questions Notes List the structures found in the nervous system. What is the function of the nervous system? What are impulses? What is the name of the cells of the nervous system? What are the 3 types of neurons and what direction do the impulses travel in each? What is the largest structure in the neuron? What structure carries impulses from the environment? What do nodes do to the speed of an impulse? What are myelin sheaths?

I. Overview of the Nervous System • Structures: ___________, spinal cord, & peripheral nerves • Function: Recognizes and ______________the body’s

________________________ in its internal and external environments

• The ultimate control of all the organ systems is done by the ___________________ system.

A. Neurons • _____________ are ______________ cells that carry

electrical __________________ through the body. • Impulse = ___________________ • Neurons are classified according to the

_____________________ an impulse travels • There are 3 types of neurons:

– 1) _______________ neurons: carry impulses from the ____________________ to the brain.

– 2) ______________ neurons: carry impulses from the _________________ to muscles and glands.

– 3) _________________: connect sensory and motor neurons and process impulses (found mainly in the brain and spinal cord)

B. Structure of a Neuron (In order of the path of the impulse)

1. _________________: receives impulses

2. __________ _________: contains nucleus & cytoplasm, largest part of cell

3. ____________: transmit impulses away from cell body

4. _____________ _____________: covering that insulates the axon, sending

the impulse faster and gives axons a _______________ appearance

• Neurons with axons that have myelin make up “_________________” in the brain, while neurons without myelin are called “________________”.

5. __________: gaps in the myelin sheath where membrane is exposed. Impulses jump from one node to the next

6. _________ _____________: transmits impulse (message) to next cell

What is the charge in and out of the cell in a resting neuron? What 2 molecules are responsible for starting an action potential?

What happens when the neuron becomes stimulated? What is an action potential? Where does the impulse travel?

II. Transmission of an Impulse • A nerve impulse is an electrical

message. • At rest, no impulse is being sent. • The neuron must be stimulated

(receive input) to send an impulse. A. Resting Neuron

• STEP 1: At rest, the neuron is __________________________ an impulse. o inside of neuron has a net ______________ charge (-) o outside of neuron has a net

_____________ charge (+) • The cell membrane has

_________________________, the potential to carry and electrical current because there is a difference in charge.

o The ions ______________ (Na+) and ____________ (K+) cause the potential

• __________________________ in the nerve cell membrane pumps _____________ (Na+) ions _____ of the cell and ______________ (K+) ions ________ the cell by means of active transport.

• As a result, the inside of the cell contains more K+ ions and fewer Na+ ions than the outside.

B. Stimulated Neuron • STEP 2: An impulse begins when a ________________________________ by

another neuron or by the environment. o The stimulated impulse must reach _________________, the minimum

impulse strength needed to create a new impulse (all or none) • STEP 3: At the leading edge of the impulse, gates in the sodium channels open

allowing positively charged ______________ (Na+) ions to flow ___________ the cell membrane.

• This ______________ of charges is called a nerve impulse, or an _______________________ (AP).

• As the action potential passes, gates in the potassium channels open, allowing _____________________ (K+) ions to flow ________________

o This restores the negative potential inside the axon.

• STEP 4: The AP jumps from node to _________ along the axon

• STEP 5: The AP continues along the axon in one direction to the ________________

C. Synapse

Nervous System Chapter 35.2

Where does the transfer of an impulse occur? What are neurotransmitters? Describe the steps of transmitting an impulse from one neuron to the next. What is re-uptake? Compare and contrast excitatory vs. inhibitory NTs? What is the effect of GABA? What is glutamate involved with? What are the effects of dopamine? How is it involved in addiction? What does serotonin regulate?

• Synapse: the space where the axon terminal of one neuron can transfer and impulse to ________________________

o The small space between cells is called the synaptic cleft.

o Axon terminals contain vesicles filled with _______________________.

• Neurotransmitters (NTs) are __________________ that transmit an impulse across a synapse to another cell

o NTs fit like a _________________ with receptors

• Steps of Transmission o STEP 6: _____________________

reaches the axon terminal o STEP 7: ______________________ is

released from vesicles into the synaptic cleft

o STEP 8: Neurotransmitter binds to _______________ on next neuron.

o STEP 9: Channels open, which creates a new action potential in the next neuron

• Re-uptake of Neurotransmitters o Re-uptake: after the NT has done its job, it is __________________ into

the axon terminal so it can be used again or broken down.

III. Types & Effects of Neurotransmitters (NTs) • There are dozens of different NTs, but a few do most of the work. • Each NT fits with its own specific receptor.

o It won’t cause a response without the right receptor. • NTs can be excitatory or inhibitory

o Excitatory NTs __________________ in the next neuron o Inhibitory NTs __________ and impulse from being sent in the next neuron

• Major Neurotransmitters • 1) GABA – Inhibitory

o Effects: ________________, calming, anti-anxiety, and sleep o Depressant drugs like heroin, marijuana, and alcohol intensify effects of

GABA • 2) Glutamate – Excitatory

o Effects: Stimulates __________________________________ formation o Some drugs can interfere with glutamate, causing short-term memories not

to be formed • 3) Dopamine – Excitatory

o Effects: ______________, Euphoria, Reward-centers, addiction, positive reinforcement, movement and posture

o Most addictive drugs (cocaine, PCP, heroin, opiates, marijuana, and amphetamines) work by flooding the synapse with dopamine

• 4) Serotonin – Excitatory

When are endorphins inhibitory? How do drugs interfere with NTs? What is addiction?

o Effects: Sleep, ____________, appetite, pain, body temperature o Low serotonin linked to depression, suicide, impulsive behavior, and aggression o Alcohol, stimulants, marijuana and hallucinogens alter serotonin levels

• 5) Endorphins – Excitatory & Inhibitory o Effects: alertness, blocks pain, happy (runner’s high), sexual arousal o Often released after physical activity

• 6) Norepinephrine – Excitatory o Effects: alertness, energy, stress, sexual arousal

• 7) Acetylcholine – Excitatory o Effects: alertness, memory, muscle contraction, appetite, sexual arousal

IV. Effects of Drugs • Many prescription and illegal drugs can alter the brain’s chemistry.

o Many drugs are ______________ (enhancers) of certain neurotransmitters that cause many of the pleasurable sensations of drugs and lead to addiction.

o Addiction: chemical dependency on a substance as a result of it altering the brain’s chemistry after repeated use.

• Ways Drugs interfere with Neurotransmission o 1) Increase number of impulses o 2) Release NT from vesicles with or without an impulse o 3) Block reuptake or block receptors o 4) Produce more or less NT o 5) Prevent vesicles from releasing NT

Learning Goals

1. Describe the function and main structures of the nervous system. 2. Describe the state of a resting neuron, including the charges inside and outside the cell. 3. Explain how an impulse is sent through a neuron, including what an action potential is. 4. Explain how an impulse is sent from one neuron to the next at the synapse, including the

role of neurotransmitters.